While there has been an increasing need for high density memory systems capable of storing large amounts of information and accessible at high speeds optical recording elements capable of optically recording, erasing and playing back information have begun to attract attention. Research and development especially aimed at improving DRAW (Direct Read After Write) type optical disks, rewritable optical disks and portable memory cards are expedited in order to find wide applications for the optical recording elements.
Conventionally, a multiple-layer construction having anti-reflection properties is widely employed in such optical recording elements. With reference to FIGS. 5(a)-5(c), optical recording elements of multiple-layer construction, are known and including (i) optical recording elements comprising a recording medium 20 formed on one face of a transparent substrate 14, the recording medium 20 including a recording layer 11, transparent dielectrical layer 12 and reflective film layer 13 (see FIG. 5(a)); (ii) optical recording elements comprising a recording medium 21 dormed on one face of the transparent substrate 14, the recording medium 21 including two transparent dielectric layers 15 and 16, and the recording layer 11 (see FIG. 5(b)); and (iii) optical recording elements comprising a recording medium 22 formed on one face of the transparent substrate 14, the recording medium 22 including two transparent dieletric layers 17 and 18, the recording layer 11, and the reflective film layer 13 (see FIG. 5(c)). These types of optical recording elements have anti-reflection properties exhibited by the interference effect of the transparent dielectric layers 12, 15, 16, 17 and 18, respectively.
In DRAW type optical recording elements, e.g. punching type optical recording elements, the anti-reflection properties acheived by the multiple-layer construction is essential for enhancing the contrast in the reproduced information and obtaining high recording sensitivity. Also, the above anti-reflection properties are required in a magneto-optical recording element, in order to improve the element's playback performance by enhancing the magneto-optical effects.
The aforesaid transparent substrate 14 is made of a plastic such as polycarbonate resin, glass ot the like. In particular, it is possible to economically produce large quantities of the substrates 14 made of a plastic at low cost by injection molding or similar methods, and therefore such substrates 14 are widely used. The recording layer 11 is comprised of, for example, an amorphous rare earth-transition metal thin film such as GdTbFe which is suitable for magneto-optical recording.
Although the recording and playback performances of the optical recording elements can be improved by the conventional constructions, the amount of reflected light from the recording layer 11 is inevitably decreased since it is required to effectively cause the interference of light at the abovementioned transparent dieleletric layers 12, 15, 16, 17 and 18. Therefore, the optical recording element having any of the above constructions has a dark tone appearance, and shows up badly in comparison with disks in which a material having metalic luster is used for obtaining a high reflective factor such as compact disks and video disks for playback use only; and magnetic cards having a colorful design provided thereon such as cash cards, credit cards and various prepaid cards.
The transparent substrate 14 composing the conventional optical recording element tends to generate a static charge, as apparent from the fact that the optical recording element having the transparent substrate 14 of polycarbonate resin shows a specific resistance of approximately 1.times.10.sup.16 .OMEGA..multidot. cm on the surface thereof. Since the surface of the transparent substrate 14 easily gets dust because of the static charge, noise is generated deteriorating the reliability of the optical recording element.